Let me start by saying that our wine does not, and should not, have a problem with tartrate crystals! I just thought that I would talk about tartrate because it's a topical subject for us at the moment - I shall explain why.....
When a wine is chilled (in your fridge for example), it can precipitate tartrate crystals - they can look pretty nasty, like sugar or even glass crystals, but in reality they are completely harmless. They are in fact potassium bitartrate, or cream of tartare (as found in baking powder) and if you find any in your wine it is still perfectly safe to drink - just pour it with a little more care, decant it, or perhaps use a strainer!
OK, so how do we prevent this? Well, actually, we don't - we make it happen in the bodega to ensure that it does not happen in your glass. This is done by passing the wine through a large freezing unit at a temperature of about -5°C, and then holding it at this temperature in special thermal tanks for between one and two weeks. The clean wine is then drawn off (racked) leaving the crystals at the bottom of the tank.
By the way, the reason that this is a topical subject is because the refrigeration equipment in our Bodega used for this process recently broke down, and cost us an arm and a leg to fix. So if you spot any one-legged wine makers hopping around, don't worry - they're quite 'armless! (sorry)